Methacrylate polymer concrete mix (MPC) has been employed to patch and repair concrete surfaces, such as roadways, sidewalks, runways and flooring. For example, MPC material is described in British Pat. No. 983,826. To form a patch of MPC, methacrylate monomer is mixed with an aggregate and subsequently polymerized in situ after filling or covering the concrete area to be patched.
Once an initiator (usually a peroxide) and a promoter (usually an aromatic amine) have been added to the methacrylate monomer, polymerization takes place rapidly, in an hour or less in a typical case. For this reason it is a common practice to blend promoter with methacrylate monomer liquid and to blend peroxide initiator with aggregate, and to combine the two blends at the repair site just prior to pouring the combined MPC (mix) into or onto the patch area. Alternatively, but less desirably, aggregate can be placed in or on the area to be repaired, and peroxide initiator added to liquid methacrylate monomer mixture which already contains promoter, and this liquid mixture poured over the aggregate so as to wet the aggregate particles.
Commonly, the aggregate (sometimes referred to hereinafter as powder mixture) will contain inorganic fillers such as silica, clays, silicates, hydrated alumina, or carbonates of various particle sizes, colorants such as titanium dioxide and/or iron oxide, a polymerization initiator for methyl methacrylate monomer, a small amount of a plasticizer such as an organophosphate and a small amount of a methacrylate polymer. Commonly, also, the monomer liquid (referred to hereinafter as liquid mixture) will contain mostly methacrylate monomer along with a small amount of a polymerization promoter such as N,N-dimethyl toluidine.
At the repair site, the aggregate and the monomer mixture, i.e., liquid mixture, are combined, mixed, and poured onto the patch area. The polymerization initiator in the aggregate initiates polymerization of the methacrylate monomer and the combined mixture, which is MPC, begins to cure through polymerization of the methacrylate. Upon completion of polymerization, the cured material is hard and concretelike.
It is known that a blend of particulate silica in the aggregate, in which the particulate is of varying sizes, is useful in reducing the spaces, of voids, between the particles. A packing material, such as calcium carbonate, may also be a part of the aggregate and aids in reducing the total void content. It is desirable to reduce the void content because, as the void content decreases, less monomer liquid is needed in the MPC. Less monomer liquid is desirable because the volume of the polymer formed is less than the volume of the corresponding monomer needed to form the polymer. Thus shrinkage occurs as the polymerization is carried out.
Even when the methacrylate liquid monomer concentration in the MPC has been reduced to a practical minimum which still meets troweling requirements (e.g., 4 to 7% methacrylate), the unrestrained shrinkage of such a casting has been determined to be about 0.20% or more. As a result, this shrinkage has caused cracking during cure of the MPC in large repairs or alternately has imparted built-in stress which has led to early failure under heavy service conditions in some cases.
The addition of a paraffinic oil to the formulation has reduced the cracking tendency of MPC in small repairs. However, the presence of paraffinic oil did not eliminate cracking in larger repairs. Also, the presence of paraffinic oil did not reduce the percent unrestrained shrinkage during cure, which is a measure of the unrelieved stress in the MPC casting. It is highly desirable to reduce the built-in stress in MPC repairs, so that the desired longevity of many years of service can be attained.